Bacteria grown in the laboratory have three stages of growth, the lag phase in which little growth occurs, the log phase in which exponential growth occurs and the stationary phase in which growth ceases. During the transition into stationary phase, bacteria acquire numerous new physiological properties which enhance their ability to compete and survive under suboptimal conditions. For reviews, see Kolter (1992) ASM News 58:75-79; Matin (1991) Mol. Microbiol. 5:3-10; Matin et al. (1989) Ann. Rev. Microbiol. 43:293-316; and Siegele and Kolter (1992) J. Bacteriol. 174:345-348. In Escherichia coli the induction of several genes and operons in the stationary phase requires a putative sigma factor, katF or rpos. Bohannon et al. (1991) J. Bacteriol. 173:4482-4492; Lange and Hengge-Aronis (1991) Mol. Microbiol. 5:49-59; Matin (1991); and Schellhorn and Stones (1992) J. Bacteriol. 174:4769-4776. The expression of stationary-phase genes such as mcbA for microcin production and glgCA for glycogen synthesis do not require katF. Bohannon et al. (1991).
Previous studies of factors that control the glycogen biosynthesis genes in E. coli showed that cyclic AMP (cAMP), cAMP receptor protein, and guanosine 3'-bisphosphate 5'-bisphosphate (ppGpp) stimulate the expression of the genes for the essential enzymes of the glycogen pathway, glgC (encoding ADPglucose pyrophosphorylase [EC 2.7.7.27]) and glgA (encoding glycogen synthase [EC 2.4.1.21]) which are apparently cotranscribed in an operon, glgCAY. Romeo et al. (1990) Curr. Microbiol. 21:131-137; and Romeo and Priess (1989) J. Bacteriol. 171:2773-2782. This operon also includes the gene encoding the catabolic enzyme glycogen phosphorylase [E.C 2.4.1.1], glgY or glgP. Romeo et al. (1988) Gene 70:363-376; and Yu et al. (1988) J. Biol. Chem. 263:13706-13711.
The gene glgB (encoding glycogen branching enzyme [EC 2.4.1.18]) is located upstream from glgCAY, apparently in an operon, glgBX, that includes a gene encoding a second catabolic enzyme. Baecker et al. (1986) J. Biol. Chem. 261:8738-8743; and Romeo et al. (1988). Although the expression of the three biosynthetic genes is induced in stationary phase, glgB is transcribed independently of glgCA and is not regulated by cAMP-cAMP receptor protein or ppGpp. Preiss and Romeo (1989) Adv. Microb. Physiol. 30:183-233; and Romeo and Preiss (1989). Four stationary-phase-induced transcripts have been mapped within the 0.5 kb upstream noncoding region of the glgc gene from E. coli, implying complex transcriptional regulation of glgCA. Romeo and Preiss (1989).
It would be highly advantageous to inhibit the metabolic pathway for glycogen biosynthesis and later reactions of gluconeogenesis in bacterial host cells, while stimulating anaplerotic reactions such as phosphoenolpyruvate carboxykinase in order to channel more carbon atoms into desired products such as aromatic amino acids.